Title: **Convert angles to microseconds?**

Post by:**jeffmorris** on **Nov 17, 2012, 11:53 am**

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How do I convert angles to microseconds? I know that 1000ms = 0 degrees, 1500ms = 90 degrees, and 2000ms = 180 degrees. What about 60 degrees and 120 degrees?

Title: **Re: Convert angles to microseconds?**

Post by:**retrolefty** on **Nov 17, 2012, 11:57 am**

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How do I convert angles to microseconds? I know that 1000ms = 0 degrees, 1500ms = 90 degrees, and 2000ms = 180 degrees. What about 60 degrees and 120 degrees?

Well you could use the map command.

microValue = map(angleDegrees, 0,180,1000,2000);

Lefty

Title: **Re: Convert angles to microseconds?**

Post by:**robtillaart** on **Nov 17, 2012, 02:00 pm**

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The map function will do well but might have some (small) error as it uses integer math which does rounding.

90 degrees is a step of 500. so 9 degrees is a step of 50. we can not simplify this in integer space, without rounding errors. we know 0.9 is a step of 5.

so we can do a float function

if we want no float math we can multiply the degrees by an integer const and divide the result at the end.

This can be rewritten to a oneliner

to minimize the rounding error of integer math we can add a rounding factor [which is half of the divider].

filling in 60 --> 1333

120 --> 1667

0 --> 1000

180 --> 2000

1 --> 1006

179 --> 1994

90 degrees is a step of 500. so 9 degrees is a step of 50. we can not simplify this in integer space, without rounding errors. we know 0.9 is a step of 5.

so we can do a float function

Code: [Select]

`float degree2ms(float degrees)`

{

return 1000.0 + degrees * 50.0/9.0;

}

if we want no float math we can multiply the degrees by an integer const and divide the result at the end.

Code: [Select]

unsigned int degree2ms(unsigned int degrees)

{

unsigned int rv = degrees * 3; // 0..1080

rv = rv * 50; // 0..54000

rv = rv /9; // 0..6000

rv = rv /3; // 0..200

return 1000 + rv;

}

This can be rewritten to a oneliner

Code: [Select]

unsigned int degree2ms(unsigned int degrees)

{

return 1000 + degrees * 150 / 27;

}

to minimize the rounding error of integer math we can add a rounding factor [which is half of the divider].

Code: [Select]

unsigned int degree2ms(unsigned int degrees)

{

return 1000 + (degrees * 150 + 13) / 27;

}

filling in 60 --> 1333

120 --> 1667

0 --> 1000

180 --> 2000

1 --> 1006

179 --> 1994

Title: **Re: Convert angles to microseconds?**

Post by:**zoomkat** on **Nov 17, 2012, 06:26 pm**

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I think the servo library maps degree values to microsecond values, so some tweeking might be done there.